Installation of industrial measuring and monitoring systems, such as a radar level gauge system, are often time-consuming and expensive. Such systems generally comprise a number of electronic systems, such as sensors for measurement of filling level, temperature, pressure etc. These electronic systems typically need to communicate with a central controlling unit and/or each other. During installation of such systems a substantial amount of cabling consequently has to be laid out. The environment is often difficult, perhaps with corrosive or hazardous fluids, and cables and/or cable-wall interfaces typically need to be sealed in order to provide an explosion-proof system.
Since, due to the difficult environment, cabling costs usually end up in the same range as material costs and sometimes even higher, use of wireless systems has naturally been contemplated, but so far not particularly widely used.
The cost for necessary radio hardware has in recent years decreased dramatically, and consequently this cost alone is no big obstacle for a widespread use in, for instance, high-grade industrial sensors for level, pressure, flow etc.
One of the main reasons that wireless communication is not more widespread than it is in an industrial environment, despite the previously mentioned reduced cost of hardware, is that those low-cost, mass-produced radio transmitters and receivers are generally not adapted for use in an industrial environment. Specifically, there are certain harsh requirements on electronics to be used in a hazardous environment, for example where explosive gases are potentially present in the atmosphere. The term hazardous is conventionally used to characterize such environments and special rules and regulations often applies to make electrical equipment reduce such potential danger.
Therefore, industrial wireless applications using conventional solutions today typically include a separate (explosion-proof) box containing a radio modem, an antenna and cabling. Put together, these auxiliary arrangements for achieving a unit suitable for an industrial environment will be an order of magnitude more expensive than the actual active radio hardware.
In order to enable economically viable use of wireless communication between industrial electronic units, there is thus a need for an inexpensive arrangement allowing for the use of inexpensive mass-produced radio hardware in an industrial environment.
DE 100 26 033 discloses a measurement transducer for use in a hazardous environment. The disclosed transducer is contained in a pressure-tight metal housing. The metal housing has a dielectric window, through which high-frequency signals are capacitively coupled through surface patches to an antenna on the outside of the dielectric window. The formal requirements for an encapsulation able to contain internal explosions is conventionally referred to as explosion-proof or flame-proof.
A problem confronted when designing such capacitive coupling arrangements through an explosion-proof housing is to get a sufficiently strong signal coupling while keeping the dielectric portion of the housing strong enough.
In an arrangement such as that disclosed in DE 100 26 033, the dielectric window would need to be made very thin in order the obtain a satisfactory signal-to-noise ratio of the wireless signal. As a consequence, there appears to be a non-negligible risk of mechanical failure of the housing. Thus, there is a big difficulty with this proposed design to fulfill both the mechanical strength to contain possible explosions and to enable a sufficiently good capacitive coupling.
Consequently, there is a need for a high-frequency coupling arrangement for a hazardous environment, enabling construction of a more robust explosion-proof equipment housing.